Preheat oven to 425°.
Rub an 11 x 7-inch baking dish with cut sides of garlic halves; discard garlic. Coat dish with cooking spray.
Arrange half of potatoes in dish, and drizzle with half of the butter. Sprinkle with half of salt and half of pepper, and top with half of cheese. Repeat the layers.
Bring milk to a boil over low heat in a small saucepan; pour over potato mixture. Bake for 40 minutes or until tender.